1. Field of the Invention
The present invention relates to a glass cutting method and apparatus, and more particularly to a glass cutting method and apparatus in which cutting of glass is carried out using a laser beam and a coolant while varying the moving speed and energy of the laser beam, and the shape of the laser beam, thereby being capable of achieving an increase in glass cutting speed and an improvement in glass quality.
2. Description of the Related Art
As a representative glass cutting device, a device for cutting glass using a laser is known. Such a glass cutting device using a laser cuts glass by irradiating a laser beam having an oval, U, or V shape, thereby heating the surface of the glass, and spraying a coolant just after the irradiation of the laser beam.
Referring to FIG. 1a, a conventional glass cutting method utilizing a temperature gradient is illustrated. In accordance with this method, a glass 2 is heated to a temperature not more than the melting point thereof using a laser beam 1, and a coolant 3 is sprayed onto the heated glass 2, thereby cutting the glass 2. FIG. 1b illustrates the glass cut in accordance with the glass cutting method. In FIG. 1b, the cut glass pieces are denoted by the reference numeral 2axe2x80x2. 
Another conventional glass cutting method is illustrated in FIG. 2a. In accordance with this method, a line is scratched on a glass tube 2b which is, in turn, heated by an oval laser beam emitted from a laser 1b. The heated glass tube 2b is then cooled by a cotton cloth 3b wet with water, so that it is cut along the scratched line. FIG. 2b illustrates glass tubes 2bxe2x80x2 cut by the above mentioned glass cutting method.
Another conventional glass cutting method is illustrated in FIG. 3. In accordance with this method, a glass 2c is heated by an oval laser beam emitted from a laser 1c. The heated portion of the glass 2c is then cooled by a coolant fluid 3c, thereby causing the glass 2c to be cut.
FIG. 4 illustrates another conventional laser glass cutting method in which a glass 2d is cut along a curved line using a laser 1d irradiating a U or V-shaped laser beam, and a coolant 3d. 
In accordance with the above mentioned laser glass cutting techniques, cutting of a glass is carried out by irradiating a laser beam having an oval, U, or V shape onto the glass to heat the surface of the glass, and then spraying a liquid or gas onto the heated portion of the glass to cool the heated glass portion.
Meanwhile, before the cutting of the glass 2, a scratch line is drawn, using a diamond wheel 4, on the leading or trailing portion of a cutting line, along which the glass is to be cut, in accordance with these laser glass cutting techniques, as shown in FIG. 5.
The laser 1 is then moved along the glass 2 to irradiate a laser beam onto the glass 2 formed with the scratch line, thereby heating the glass 2. Thereafter, the coolant sprayer sprays a coolant 3 onto the heated portion of the glass 2 while moving at a certain speed, thereby causing the glass to be cut.
That is, in accordance with the convention laser glass cutting techniques, cutting of glass is carried out by irradiating a laser beam from a laser with a desired energy onto the glass while moving the laser along a scratch line formed on the glass, thereby heating the glass, and spraying a coolant onto the heated portion of the glass, thereby cooling the glass. However, these conventional laser glass cutting techniques have a problem in that the cut surface of the glass is rough because the glass is heated by the laser beam which is irradiated onto the glass using a uniform energy while being moved from a leading portion of the glass to a trailing portion of the glass at a constant speed, in spite of the fact that the glass exhibits different stress distributions at respective portions thereof, that is, the leading and trailing portions, and an intermediate portion arranged between the leading and trailing portions, when it is heated. In particular, there is a problem in that it is impossible to easily cut the glass at the leading and trailing glass portions.
Where the energy density of the laser beam irradiated onto the glass at the leading and trailing glass portions is excessive, the surface of the glass may be abruptly heated, so that it is thermally damaged. As a result, the cut surface of the glass may be damaged. On the other hand, where the energy density of the irradiated laser beam is insufficient, a lot of time is undesirably taken to cut the glass.
Therefore, the present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a glass cutting method and apparatus in which cutting of glass is carried out using a laser beam while appropriately adjusting the moving speed and energy of the laser beam for respective portions of the glass, so that the glass can be rapidly and accurately cut.
Another object of the invention is to provide a glass cutting method and apparatus capable of preventing a localization of thermal stress generated at the surface of glass when a laser beam is irradiated onto the glass, thereby forming a cut glass surface having a good quality.
In accordance with one aspect, the present invention provides a glass cutting method comprising the steps of irradiating a laser beam onto a virtual cutting line on a glass to be cut while moving the laser beam along the virtual cutting line, thereby heating the glass, and spraying a coolant onto the heated glass, thereby cutting the glass, wherein the glass is divided, along the virtual cutting line, into leading, intermediate, and trailing portions, and the laser beam has a moving speed and energy controlled so that the moving speed and energy are gradually increased as the laser beam moves from the leading glass portion to the intermediate glass portion, while being gradually decreased as the laser beam moves from the intermediate glass portion to the trailing glass portion.
In accordance with another aspect, the present invention provides a glass cutting apparatus comprising: a first beam generating unit for irradiating a laser beam to form scratch lines on a glass to be machined; a second beam generating unit for irradiating a primary laser beam onto the glass 11 to heat the glass along the scratch lines; and a coolant sprayer for spraying a coolant onto the glass to cut the heated glass.
Each of the leading, intermediate, and trailing glass portions may be divided into a plurality of sub-portions, the moving speed and energy of the laser beam being constant within each of the sub-portions.
The moving speed of the laser beam may be varied proportionally to a variation in energy density of the laser beam.
The laser beam may have a leading portion and a trailing portion respectively forming, on the glass, an image having a leading portion with a large area, and a trailing portion with a small area. In this case, the leading image portion has an energy density less than that of the trailing image portion.
Preferably, the laser beam has a key hole shape.